There are already known in the art quick closure couplings for hydraulic lines comprising a plug valve and a sleeve valve, each with a closure piece held in the closed position by spring action. Such couplings are used, for instance, for the coupling of accessory devices to the hydraulic system of utility vehicles.
In order to make possible the coupling and uncoupling of a pressureless coupling half with a pressure-loaded coupling half, the closure piece of the coupling half on the pressureless side can be moved by twice the opening stroke while the opening stroke of the closure piece of the other coupling half is limited by a stop which is contacted by the closure piece in the opening position. Since the closure piece of the coupling half on the pressure side is under spring pressure and flow medium pressure, this closure piece remains at rest during coupling and the closure piece, displaceable by twice the opening stroke, of the other coupling half undergoes an axial displacement exceeding the single opening stroke. If flow medium pressure is applied to the coupling half which first was pressureless during coupling, there appears pressure compensation between the two closure pieces and they attain their opening positions under the action of the closure spring of the closure piece first displaced by twice the opening stroke; as a rule, this spring is stronger than the closure spring in the other coupling half. This opens the flow through such a coupling.
The trouble with these couplings appears to be that in the opening position the closure piece, which is not held against its fixed stop and is axially movable by twice the double opening stroke, it is so-to-speak floating and can make axial movements beyond its single opening position, depending on operating conditions, especially with pressure surges. These axial movements of this closure piece of one coupling half are followed by the closure piece of the other coupling half; in this latter coupling half, there will develop changes in the flow cross-section and hence undesirable changes of the flow conditions in the coupling. Under extreme operating conditions there may be an unwanted closing of the valve, completely blocking the entire hydraulic system.
Many attempts have been made to eliminate the hazard of unwanted closing of such valves under extreme operating conditions. However, these attempts were rather unsuccessful. In particular, the attempt has been made to design the closure springs of the two coupling halves in such a way that the closure piece, axially closable via the double opening stroke, after the opening of the valves is held in a stable opening position in the operating range under consideration. Satisfactory results were obtained for normal operation; however, operational safety under extreme conditions, eliminating a sudden closure of such a flow medium coupling, was not achieved.
This defect will be remedied by the invention. It is an object to improve such couplings in such a way that they cannot be closed when pressure is applied to one coupling half, even during pressure surges, reversals of the flow direction and high flow rates, without impairing their ability to be coupled.
Another object of the present invention is to provide an arrangement of the foregoing character which is substantially simple in construction and may be economically fabricated.
A further object of the present invention is to provide a quick-closure arrangement, as described, which may be readily maintained in service and which has a substantially long operating life.